The catalysis or inhibition of the hydrolysis of phosphate esters is being examined especially from the point of view of reaction occurring at an interface between water and a lipid-like region, for example at the surface of a micelle of a synthetic or naturally occurring surfactant. The substrates generally will be acyl or aryl phosphates, and potentially reactive nucleophilic, acidic or basic groups will be located at the interface. One aim of the work will be to control not only the rate of the reaction, but also the products by varying the nature of the interface, for example interactions between quaternary ammonium ions and pi-electron rich groups seem to be very important in these systems. Another beneficial type of interaction is observed when an unfavorable Coulombic interaction is set up in the initial state and disappears in the transition state, and this mechanism of catalysis is also being investigated as a model for one aspect of enzymic catalysis.